Dedicated riser tensioner apparatus, method and system

ABSTRACT

The invention is an apparatus, method and system for supporting risers in a floating platform. The apparatus comprises a table disposed above a hull-top surface, a first riser opening in the table, and a first dedicated riser tensioner attached to the table and disposed about the first riser opening. The apparatus further comprises a second riser opening, and a second dedicated riser tensioner attached to the table and disposed about the second riser opening. The method comprises tensioning a first riser with a first dedicated riser tensioner, and tensioning a second riser with a second dedicated riser tensioner, wherein the first dedicated riser tensioner is responsive to the second dedicated riser tensioner. The system comprises means for tensioning a first and a second riser, wherein the means for tensioning the first riser is responsive to the second riser.

BACKGROUND OF THE INVENTION

[0001] Drilling and production operations for the exploration and production of offshore minerals require a floating platform that is as stable as possible against environmental forces. To avoid fatigue on the risers, some floating platforms (e.g., Spars) have drilling and production risers that are supported by buoyancy “cans” attached to each of the individual risers. As the water depth increases, larger buoyancy cans are used to support the in-water weight of the risers. Larger buoyancy cans require larger center-wells, which, in turn, increase the hull diameter. Increasing the hull diameter increases the hydrodynamic environmental loads acting on the platform. A larger mooring system is then required to withstand the increased environmental loads. These undesirable effects increase the fabrication and installation costs.

[0002] With present buoyancy can riser support systems, as the hull displaces laterally in response to environmental loads, the risers undergo a considerable amount of downward motion, or pull-down, with respect to the hull. Counterbalancing these environmental loads is crucial in order to avoid destruction of the risers or the platform. Counterbalancing environmental loads by tying the risers to a single table, gimballing the risers, or both, provide some additional support, but such systems still cannot support large tensile loads possible in offshore environments.

[0003] A need, therefore, exists for an improved apparatus, method and system that support drilling and production risers.

SUMMARY OF THE INVENTION

[0004] The described problems in supporting drilling and production risers are addressed by an apparatus, method and system having a dedicated riser tensioner for each riser, thereby allowing each riser to move vertically independently of the other risers without requiring gimballing. Further, the invention cross-couples the dedicated riser tensioners as a way to soften motions other than heave.

[0005] According to one aspect of the present invention, an apparatus is provided for supporting risers in a floating platform. The apparatus comprises a table disposed above a hull-top surface, a first riser opening in the table, and a first dedicated riser tensioner attached to the table and disposed about the first riser opening. The apparatus further comprises a second riser opening, and a second dedicated riser tensioner attached to the table and disposed about the second riser opening.

[0006] According to another aspect of the invention, a method is provided for supporting risers in a floating platform. The method comprises tensioning a first riser with a first dedicated riser tensioner. In addition, the method comprises tensioning a second riser with a second dedicated riser tensioner, wherein the first dedicated riser tensioner is responsive to the second dedicated riser tensioner.

[0007] According to another aspect of the invention, a system is provided for supporting risers in a floating platform. The system comprises a means for tensioning a first riser and a means for tensioning a second riser, wherein the means for tensioning a first riser is responsive to a means for tensioning a second riser.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a cross-section of an example embodiment of the invention showing a Spar-type floating platform showing the risers and dedicated riser tensioners.

[0009]FIG. 2 is a top view of an example embodiment of the invention showing a Spar-type floating platform having a table, riser openings, risers, pull tube openings, pull tubes, miscellaneous openings, access shaft, and the Spar-hull.

[0010]FIG. 3 is a schematic view of an example embodiment of the invention showing a cross-coupling arrangement between the dedicated riser tensioners.

[0011]FIG. 4 is a schematic view of an example embodiment of the invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0012] Referring now to FIG. 1, an apparatus for supporting risers 10 a and 10 b in a Spar-type floating platform 15 is seen. A table 18 is disposed above a hull top surface 21 and includes a first riser opening 25 a and a first dedicated riser tensioner 27 a that is attached to the table 18 and disposed about the first riser opening 25 a. A second riser opening 25 b is also seen disposed about a second dedicated riser tensioner 27 b. In further embodiments of the invention, more than two risers 10 a and 10 b, dedicated riser tensioners 27 a and 27 b, and riser openings 25 are used.

[0013] Turning now to FIG. 2, another example embodiment of the invention is seen in which the table 18 comprises a grid 30. The grid 30 has rows 31 and columns 32 that intersect to form square areas 35. Further, each of these areas 35 is capable of having one of the riser openings 25 to accept a riser 10 a and 10 b (seen in FIG. 1). Further still, every area 35 need not be utilized on the table 18. In the example embodiment shown in FIG. 2, the areas 35 that have riser openings 25 comprise a quincunxial arrangement 38, whereby a grid 40, having three rows 31 and three columns 32, is formed. A “quincunxial arrangement” is identical to the dot representation of the number five on a standard die.

[0014] The four lateral sides 33 of the grid 40 further comprise a linear arrangement 39 of three areas 35 having riser openings 25 adjoining each one of the sides 33. That is, as opposed to the top or bottom sides of the grid 40, each of the four lateral sides 33 of the grid 40 have three areas 35. As seen, riser openings 25 are in a linear arrangement 39 and are adjoined to each one of the sides 33 of the grid 40.

[0015] Other example embodiments of the invention comprise sizes, numbers, and shapes of the areas 35 that are different from the gridwork on the table 18. Further, other example embodiments include different numbers and types of riser openings 25 in the table 18.

[0016] Referring now to FIGS. 1 and 2, in some example embodiments of the invention, at least one of the risers 10 a and/or 10 b comprises a drilling riser. According to alternative embodiments, at least one of the risers 10 a and/or 10 b comprises a production riser. Further, variations in the number of risers 10 a and 10 b are within the scope and spirit of the invention. However, each of the risers 10 a and 10 b is tensioned by a dedicated riser tensioner 27 a and 27 b,whether the riser is a production riser or a drilling riser.

[0017] Focusing now on FIG. 2, according to another example embodiment of the invention, the dedicated riser tensioners 27 a and 27 b comprise a plurality of cylinders 28. The plurality of cylinders 28, in some embodiments, comprises four cylinders 28 coupled to each production riser 10 b. In some examples, the cylinders 28 comprise pneumatic cylinders; while, in other embodiments, cylinders 28 comprise hydraulic cylinders. Other types of cylinders 28 are useful in other example embodiments of the invention, as are mixtures of the types of cylinders 28.

[0018] A plurality of pull tubes 50 is dispersed near the edges of the table 18. The pull tubes 50 comprise at least one flowline pull tube 52, at least one export gas pull tube 54, at least one export oil pull tube 56, at least one commercial umbilical pull tube 58, and at least one umbilical pull tube 60. Inclusion or exclusion of some or all of these pull tubes 50 are useful according to various embodiments, as are other pull tubes 50 not specifically mentioned.

[0019] A plurality of openings 65 are dispersed near the edges of the table 18. According to some such example embodiments, the following are provided: at least one seawater opening 67, at least one jockey opening 70, at least one seachest feed 71, and at least one access shaft 73. Inclusion or exclusion of some or all of these openings 65 is within the scope of the present invention, as are other openings 65 not specifically mentioned above.

[0020] Now referring to FIGS. 1 and 3, according to other example embodiments of the invention, at least a first dedicated riser tensioner 27 b and a second dedicated riser tensioner 27 b are engaged in a cross-coupling arrangement 75. While it is production dedicated riser tensioners 27 b engaged in cross-coupling arrangements 75, as shown, other types of dedicated riser tensioners (e.g., drilling riser tensioners) are cross-coupled in other embodiments of the invention. Further, more than two risers tensioners 27 a and 27 b are engaged in a cross-coupling arrangement in alternative embodiments. For example, as shown in FIG. 3, sixteen dedicated riser tensioners 27 a and 27 b are engaged in a cross coupling arrangement. In the illustrated example, each of the riser tensioners 27 b comprises a set 28 a of cylinders 28 for supporting a production riser 10 b; therefore, there are multiple sets 28 b of cylinders 28 for supporting multiple risers 10 b. It is these multiple sets 28 b of cylinders 28 that are the subject of the cross-coupling arrangement 75 and form a cross-coupling circuit 91. In one example embodiment of the invention, there is a symmetrical pairing 81 of each cylinder 28 in the set 28 a of cylinders 28 with other cylinders 28 in the multiple sets 28 b of cylinders 28. In various embodiments, symmetry in pairing the cylinders 28 balances counteracting environmental loads. In the illustrated example, a cross-coupling arrangement 75 of the cylinders 28 comprises symmetrical pairing 81 by rows 31, and a point of reference for the symmetrical pairing 81 by rows 31 determined from the center of the grid 30.

[0021] To elaborate on the cross-coupling arrangement 75 involving symmetrical pairing 81 by rows 31, a table entitled “Tensioner Interconnecting Plumbing” appears on FIG. 3. Referring to that table, under “Row Pairing,” it is seen that the cylinders 28 in rows A and E are paired with each other, the cylinders 28 in rows B and D are paired with each other, and the cylinders 28 in row C are paired with themselves. Similarly, in further embodiments of the invention, table 18 is expanded by two rows 31, so that the cylinders 28 have the following pairing: rows A and G, rows B and F, rows C and E, and row D with row D. Finally, it should be noted that in the specific embodiment shown, each one of the four cylinders 28 in the set 28 a is located near a different one of the four vertices 79 within each one of the substantially square areas 35.

[0022] Under “Column Pairing,” it is seen that the cylinders 28 in columns 1 and 5 are paired with each other, the cylinders 28 in columns 2 and 4 are paired with each other, and the cylinders 28 in column 3 are paired with themselves. Similarly, in further embodiments of the invention, table 18 is expanded, for example, by two columns 32, so that the cylinders 28 have the following pairing: columns 1 and 7, columns 2 and 6, columns 3 and 5, and column 4 with column 4. As with the symmetrical pairing 81 by rows 31, the symmetrical pairing 81 by columns 32 may form cross-coupling arrangements 75 not explicitly disclosed, but are deemed to be implicitly disclosed because such cross-coupling arrangements 75 are within the same spirit and scope as the invention.

[0023] Under “Position Number Pairing,” it is seen that a cylinder 28 in position 1 is paired with another cylinder 28 in position 1, a cylinder 28 in position 2 is paired with another cylinder 28 in position 2, a cylinder 28 in position 3 is paired with another cylinder 28 in position 3, and so forth. Similarly, in further examples, table 18 is expanded, such as by two cylinders 28, wherein the symmetrical pairing 81 by identical position-number 85 remains the same in kind, but differs only in amount of position numbers 85 to be paired. As with the symmetrical pairing 81 by rows 31 and by columns 32, although other position-number cross-coupling arrangements 75 are used in other embodiments of the invention.

[0024] Turning now to other aspects of the invention, a method and a system for supporting risers in a floating platform are disclosed. Although only the system is discussed below, the previous and foregoing discussions are understood to enable both the method and system disclosed herein.

[0025] Accordingly, in one example embodiment, as seen in FIG. 4, a system 100 is disclosed for supporting a first riser 105 and a second riser 110 with a floating platform 115. The system 100 comprises a means 125 for tensioning the first riser 105 in response to an environmental load 130, and a means 135 for tensioning the second riser 110 in response to the same environmental load 130.

[0026] The means 125 for tensioning the first riser 105 is responsive to the means 135 for tensioning the second riser 110 in that the system 100 comprises the above-described apparatus 15, wherein FIGS. 2 and 3 show a cross-coupling arrangement 75 between the cylinders 28 that make up the dedicated riser tensioners 27 a and 27 b for each and every one of the risers 10 a and 10 b. Stated in terms of the system 100, the means 125 and 135 comprise the dedicated riser tensioners 27 a and 27 b for the first riser 105, the second riser 110, and all other risers 10 a and 10 b. In addition, the means 125 and 135 provide a counteracting force 140 in order to support and prevent destruction of risers 10 a and 10 b, wherein the counteracting force 140 opposes an environmental load, such as a wave, incident on the floating platform 115.

[0027] Having thus described exemplary embodiments of the invention, it will be apparent that various alterations, modifications and improvements will readily occur to those skilled in the art. Such obvious alterations, modifications and improvements, though not expressly described above, are nevertheless intended to be implied and are within the spirit and scope of the invention. Accordingly, the foregoing discussion is intended to be illustrative only, and not limiting; the invention is limited and defined by the following claims and equivalents thereto. 

What is claimed is:
 1. An apparatus for supporting risers in a floating platform, the apparatus comprising: a table disposed above a hull-top surface; a first riser opening in the table; a first dedicated riser tensioner attached to the table and disposed about the first riser opening; a second riser opening in the table; and a second dedicated riser tensioner attached to the table and disposed about the second riser opening.
 2. The apparatus of claim 1, wherein the apparatus comprises more than two riser openings in the table.
 3. The apparatus of claim 2, wherein the apparatus comprises more than two dedicated riser tensioners, wherein each of the more than two dedicated riser tensioners are attached to the table and disposed about a different one of the more than two riser openings.
 4. The apparatus of claim 1, wherein the table comprises a grid having rows and columns intersecting to form substantially square areas, wherein each of the substantially square areas is capable of having one of the riser openings.
 5. The apparatus of claim 4, wherein the substantially square areas having the riser openings comprise a quincunxial arrangement, whereby a substantially square grid having three rows and three columns is formed.
 6. The apparatus of claim 5, wherein each one of the four lateral sides of the substantially square grid a linear arrangement of three substantially square areas having riser openings adjoining each one of the four lateral sides.
 7. The apparatus of claim 5, wherein the one of the risers passing through the one of the riser openings located at the center of the quincunxial arrangement comprises a drilling riser.
 8. The apparatus of claim 7, wherein the risers passing vertically through the riser openings not located at the center of the quincunxial arrangement comprise production risers.
 9. The apparatus of claim 4, wherein the substantially square areas have lateral sides with lengths of eleven feet and six inches.
 10. The apparatus of claim 1, wherein the apparatus comprises at least one drilling riser.
 11. The apparatus of claim 1, wherein the apparatus comprises at least one production riser.
 12. The apparatus of claim 1, wherein the apparatus comprises at least one drilling dedicated riser tensioner.
 13. The apparatus of claim 1, wherein the apparatus comprises at least one production dedicated riser tensioner.
 14. The apparatus of claim 1, wherein the dedicated riser tensioners comprise a plurality of cylinders.
 15. The apparatus of claim 14, wherein the plurality of cylinders comprises four cylinders coupled to each production riser.
 16. The apparatus of claim 14, wherein the cylinders comprise pneumatic cylinders.
 17. The apparatus of claim 14, wherein the cylinders comprise hydraulic cylinders.
 18. The apparatus of claim 1, wherein the table further comprises a plurality of pull tubes dispersed near the edges of the table.
 19. The apparatus of claim 18, wherein at least one of the plurality of pull tubes comprises at least one flowline pull tube.
 20. The apparatus of claim 18, wherein at least one of the plurality of pull tubes comprises at least one export gas pull tube.
 21. The apparatus of claim 18, wherein at least one of the plurality of pull tubes comprises at least one export oil pull tube.
 22. The apparatus of claim 18, wherein at least one of the plurality of pull tubes comprises at least one commercial umbilical pull tube.
 23. The apparatus of claim 18, wherein at least one of the plurality of pull tubes comprises at least one umbilical pull tube.
 24. The apparatus of claim 1, wherein the table further comprises a plurality of openings dispersed near the edges of the table.
 25. The apparatus of claim 24, wherein at least one of the plurality of openings comprises at least one seawater opening.
 26. The apparatus of claim 24, wherein at least one of the plurality of openings comprises at least one jockey opening.
 27. The apparatus of claim 24, wherein at least one of the plurality of openings comprises at least one seachest feed.
 28. The apparatus of claim 24, wherein at least one of the plurality of openings comprises at least one access shaft.
 29. The apparatus of claim 1, wherein the apparatus further comprises a cross-coupling arrangement at least between the first dedicated riser tensioner and the second dedicated riser tensioner, wherein each of the dedicated riser tensioners comprises a set of cylinders for supporting a production riser, thereby resulting in multiple sets of cylinders for supporting multiple production risers.
 30. The apparatus of claim 29, wherein the cross-coupling arrangement comprises a symmetrical pairing of each cylinder in the set of cylinders with other cylinders in the multiple sets of cylinders, thereby creating a cross-coupling circuit with the multiple sets of cylinder.
 31. The apparatus of claim 30, wherein the table comprises a grid having rows and columns intersecting to form substantially square areas, wherein the cross-coupling arrangement comprises the symmetrical pairing by rows, a point of reference for the symmetrical pairing by rows determined from the center of the grid.
 32. The apparatus of claim 31, wherein each one of the four cylinders in the set is located near a different one of the four vertices within each one of the substantially square areas.
 33. The apparatus of claim 30, wherein the table comprises a grid having rows and columns intersecting to form substantially square areas, wherein the cross-coupling arrangement comprises the symmetrical pairing by columns, a point of reference for the symmetrical pairing by columns determined from the center of the grid.
 34. The apparatus of claim 30, wherein the table comprises a grid having rows and columns intersecting to form substantially square areas, wherein the cross-coupling arrangement comprises a symmetrical pairing by an identical position number of each one of the cylinders in the set located within each one of the substantially square areas having one of the production risers.
 35. The apparatus of claim 1, wherein the table comprises a substantially square area having a linear side length of seventy-five feet.
 36. A method for supporting a first riser and a second riser with a floating platform, the method comprising: tensioning the first riser, with a first dedicated riser tensioner; tensioning the second riser, with a second dedicated riser tensioner; and wherein the first dedicated riser tensioner is responsive to the second dedicated riser tensioner.
 37. The method of claim 36, wherein said tensioning the first riser comprises the first dedicated riser tensioner exerting a counteracting load in response to an environmental load.
 38. The method of claim 36, wherein said tensioning the second riser comprises the second dedicated riser tensioner exerting a counteracting load in response to an environmental load.
 39. The method of claim 36, wherein the method further comprises tensioning more risers than the first riser and the second riser, wherein each of the more risers comprises a different dedicated riser tensioner in a set of dedicated riser tensioners.
 40. A system for supporting a first riser and a second riser with a floating platform, the system comprising: means for tensioning the first riser; means for tensioning the second riser; and wherein the means for tensioning the first riser is responsive to the means for tensioning the second riser.
 41. The system of claim 40, wherein the means for tensioning the first riser comprises a first dedicated riser tensioner, wherein the first dedicated riser tensioner exerts a counteracting load in response to an environmental load.
 42. The system of claim 41, wherein the first dedicated riser tensioner comprises at least two cylinders.
 43. The system of claim 40, wherein the means for tensioning the second riser comprises a second dedicated riser tensioner, wherein the second dedicated riser tensioner exerts a counteracting load in response to an environmental load.
 44. The system of claim 43, wherein the second dedicated riser tensioner comprises at least two cylinders.
 45. The system of claim 40, wherein the system further comprises means for tensioning more risers than the first riser and the second riser, wherein each of the more risers comprises a dedicated riser tensioner in a set of dedicated riser tensioners. 